In recent years, many mobile service providers have been upgrading wireless networks to support packet-switched data communications services, which extend the common data communication capabilities of the wired domain to the wireless mobile domain. A popular advantage of wireless communications is the freedom of mobility. To support mobile communication, the wireless networks perform a function called “handoff” or “handover”. Handoff is the process by which elements of a mobile network pass a cellular phone conversation or data session from one radio channel in one cell to another radio channel in another cell. It is performed so quickly that callers do not notice. Handoff, unlike roaming, involves moving an active call from one radio to another radio. Roaming involves registering for service/access through different locations on various regional networks, as a mobile station user moves.
In Code Division Multiple Access (CDMA) cellular telecommunication systems, a handoff is usually accomplished via a “soft handoff” between sectors or from one base station to another base station. In a soft handoff between base stations, for example, the mobile station is in communication with more than one base station simultaneously, and thus the mobile station performs a “make before break” transition from one base station to another base station. The soft handoff is possible because in CDMA cellular telecommunication systems, numerous mobile stations communicate with each base station on the same frequency channel, each mobile station having a unique spreading code or offset thereof for distinguishing the information signals broadcast by the numerous mobile stations. Thus, when a mobile station moves from one CDMA cell to another CDMA cell, the same frequency is used in each CDMA cell and the unique spreading code identifies the mobile station to the new base station.
A “hard handoff” occurs when it becomes necessary to handoff between systems, e.g. between systems of different service providers or between systems using different technologies (e.g. between CDMA and Advanced Mobile Phone System (AMPS), Time Division Multiple Access (TDMA) or Global System for Mobile communications (GSM) systems). The hard handoff is a “break before make” connection. The hard handoff may be necessary because the available frequency channels or the encoding technologies used in the two adjoining systems differ, and thus when a mobile station moves from one to another, a new frequency channel or coding technique must be implemented.
However, next generation radio access networks are moving away from “soft handoff” in order to more efficiently utilize radio resources. The Next Generation Network (NGN) will be dominated by asynchronous radio access networks providing only hard handoff. This makes fast and robust handoff across various radio access points extremely important.
Furthermore, current inter-Enhanced Base Station (EBS) handoff in Long Term Evolution (LTE) and inter-Access Point (AP) handoff in Worldwide Interoperability for Microwave Access (WiMAX) only defines and prepares one potential Target EBS. However, for example, when only one potential Target EBS is prepared, latency in handoff can result. In LTE and WiMAX, when a handoff is prepared, only one potential Target EBS is prepared for the handoff. Afterwards, if a signal interruption results between the Target EBS and the mobile station such that the mobile station cannot connect to the Target EBS, then the mobile station will remain connected to the Serving EBS. However, since only one potential Target EBS was prepared, then the Serving EBS will have to prepare another Target EBS for a handoff. This preparation takes time and results in the mobile station remaining connected to the Serving EBS longer than needed. This further consumes system resources. This results in system latency and poor handoff performance. However, the current LTE and WiMAX approaches result in poor handoff performance.
Additionally, Ultra Mobile Broadband (UMB) is a synchronized network which stores dual radio stacks at both Serving and Target EBS, which results in complicated terminal equipment.
Hence a need exists for a means to more efficiently determine and transfer call context information to multiple EBSs to ensure a fast and robust handoff mechanism that minimizes latency, handoff interruption and outage performance without actively involving multiple EBSs.